FUN BY YOURSELF!
If you're juggling by yourself, what you'll want to do is get into a suit of armor that allows you to carry a lot of weapons. You can juggle with even just a couple objects if you like but the juggling isn't very fast-paced then. After getting all your equipment together (as many weapons or as much ammo -depending on which you'll be tossing around- as you want to throw), make sure you know which buttons to press to switch weapons (if juggling weapons, not ammo) and change weapons. Next, find someplace you can stand without having to worry too much about being blown to pieces.

Now comes the fun part: Face straight up and quickly alternate between throwing your weapon and switching to the next weapon. If you have enough weaponry on you, the first weapon thrown should fall back into your inventory before your last weapon is thrown. What happens is that when the weapons fall back down to you, they return to your inventory. Since you'll be switching to another weapon after each throw, you'll be constantly tossing them back up as they come back down. You'll probably want to watch someone else do it or get someone to take a screenshot for you too, as it's a rather entertaining sight. Attempting to switch to the third-person view for this doesn't show much, as you'll merely be looking up into your avatar's crotch (since you're set to look straight up and the third·person camera angle is set to look whichever way you're looking from slightly behind the avatar).

For this, everyone involved should get set up the way a lone Tribes juggler would (lots of weapons, ammo, etc.). Once that's done, it's recommended a flat surface be found to do this on, as having everyone at different altitudes can cause the projectiles to miss their targets if the throwers' aim is off. Also, everyone should figure out who they're going to toss their weapons or ammo too (only select one other person to throw to). No two people should be tossing to each other directly unless only two people are involved.

What should happen with this group juggling activity is that as each player tosses his/her weapons/ammo to the next, someone else will be tossing that first player more objects to toss around. This keeps the supply of projectiles constant for everyone as they toss them all about to each other. Be warned though, someone moving out of the chain of jugglers will mean that everyone would eventually run out of things to throw (if everyone else continued tossing and switching after that one person moved) and there would be a pile of weaponry (or ammunition) on the ground where the juggler that moved once stood.

ADVANCED TACTICS
Think you and your fellow performers have taken basic team juggling as far as it can go? Perhaps you haven't. Have you tried...